1. Field of the Invention
The present invention relates to portable communications equipment that utilizes retractable or fixed antennas. More particularly the present invention relates to a transceiver device compatible with both high impedance and low impedance connections without having a matching circuit or switching means included within the device.
2. Problems in the Art
Many devices such as cellular telephones use a retractable 1/2 wave antenna. This antenna has a high impedance and requires the use of a matching circuit when connected to the transmitter to provide the maximum energy transfer to the antenna. In some prior art devices, the manufacturers add additional space to the device which is required in order to fit in a matching circuit section that may be external to the main circuit board. Also, when the output power from the transmitter or the receiver sensitivity is checked by connecting the device to testing equipment, the high impedance matching circuit presents a problem. The impedance of most testing equipment is either 50 or 75 ohms and not the high impedance required by the matching circuit (typically 600-2,000 ohms). If the transceiver performance is measured with this impedance mismatch, significant errors in the measurement will result. Many prior art devices overcome these errors by attaching an additional connector, typically coaxial, to a 50 ohm point on the transceiver circuit to provide a test point with accurate information. This solution requires additional coaxial line, a separate connector, and an electrical or mechanical switch to ensure the proper energy transfer from the printed circuit board to the chosen connection. These solutions are not desirable because of the increase in cost and circuit complexity.
Prior art devices using retractable antennas incorporate an internal matching circuit which connects to the antenna assembly to provide the performance of a 1/2 wave antenna in the extended position. The problem with this feature is that the antenna is matched to the impedance of the transceiver only in the extended position and not in the retracted position. This creates an impedance mismatch that reduces the efficiency of the antenna when it is in the retracted position.